Role of interleukin 2 on chromatin landscapes in lymph node Foxp3+ CD4+ regulatory (Treg) cells

Interleukine 2 (IL-2) is still one of the most interesting cytokines in T cell biology with its ability to control immune homeostasis by maintaining the functional identity of Foxp3+ regulatory T (Treg) cells and the expansion of activated conventional T (Tconv) cells. Yet, how IL-2 exactly enables Treg cells to suppress autoreactive Tconv cells and to maintain their identity is unclear. Using a mouse model in which IL-2 signaling via its high affinity receptor CD25 is selectively impaired, the “Il2ramut/mut” mouse, we report that Treg cells that only receive low IL-2 signals keep Il2ramut/mut but not WT Tconv cells “in check”, suggesting equal IL-2 signals in Treg and Tconv cells is essential to safeguard immune homeostasis. Furthermore, the comparative analysis of gene expression and epigenetic landscape of Il2ramut/mut and WT Treg cells support a model in which IL-2 "locks in” Treg cell identity and functions in vivo by controlling their genome-wide chromatin accessibility.